1. Field of the Invention
The present invention generally relates to rotary vane pumping machines. More particularly, the present invention relates to a hot wall combustion insert for improving combustion parameters in a rotary vane internal combustion engine.
2. Description of Related Art
This class of rotary vane combustion engines includes designs having a rotor with slots with a radial component of alignment with respect to the rotor's axis of rotation, vanes which reciprocate within these slots, and a chamber contour within which the vane tips trace their path as they rotate and reciprocate within their rotor slots.
The reciprocating vanes thus extend and retract synchronously with the relative rotation of the rotor and the shape of the chamber surface in such a way as to create cascading cells of compression and/or expansion, thereby providing the essential components of a combustion engine. For ease of discussion, a rotary vane engine will be discussed in detail.
A prior combustion design was described in pending U.S. patent application Ser. No. 08/398,443, to Mallen, filed Mar. 3, 1995, entitled "SLIDING VANE ENGINE," now issued as U.S. Pat. No. 5,524,587 on Jun. 11, 1996 (the '587 patent). The '587 patent generally describes the operation of a sliding vane engine. The operation of a vane engine using this prior combustion design will now be described.
FIG. 1 is a side cross sectional view of a conventional rotary-vane combustion engine. FIG. 2 is an unrolled view of the cross-sectional view of FIG. 1.
As shown in FIG. 1, the rotary engine assembly includes a rotor 10, a chamber ring assembly 20, and left and right linear translation ring assembly plates (not shown in full).
The rotor 10 includes a rotor shaft 11, and the rotor 10 rotates about the central axis of the rotor shaft 11 in a counterclockwise direction as shown by arrow "R" in FIG. 1. The rotor 10 has a rotational axis, at the axis of the rotor shaft 11, that is fixed relative to a stator cavity 21 contained in the chamber ring assembly 20.
The rotor 10 houses a plurality of vanes 12 in vane slots 13, and each pair of adjacent vanes 12 defines a vane cell 14. The contoured stator cavity 21 forms the roughly circular shape of the chamber outer surface.
The linear translation ring assembly plates are disposed at each axial end of the chamber ring assembly 20, and each includes a linear translation ring 31. Each linear translation ring 31 itself spins freely around a fixed hub 32 located in the linear translation ring assembly plate, with the axis of the fixed hub 32 being eccentric to the axis of rotor shaft 11.
A combustion residence chamber 26 is provided in the chamber ring assembly 20. The combustion residence chamber 26 is a cavity within the chamber ring assembly 20, radially and/or axially disposed from a vane cell 14, which communicates with air or a fuel-air charge in the vane cell 14 at about peak compression in the engine assembly. The combustion residence chamber 26 creates an extended region in communication with the vane cell 14 during peak compression.
The combustion residence chamber creates a source of ignition in the vane cell 14 where the combustion residence chamber 26 meets the vane cell 14, which ignition must spread substantially throughout the entire vane cell 14. It is important that the combustion time be of a sufficient duration for proper operation of the combustion residence chamber.
One or more fuel injecting or delivery devices 27 may be used and may be placed on one or both axial ends of the chamber and/or on the outer or inner circumference to the chamber and/or in an intake manifold upstream of the intake port to the engine. Each injector 27 may be placed at any position and angle chosen to facilitate equal distribution within the cell or vortices while preventing fuel from escaping into the exhaust stream.
Fresh intake air or a fuel-air charge, "I" is provided to the vane engine through an intake port 23 formed in the linear translation ring assembly plate and/or chamber ring 20. Similarly, combusted air or fuel-air charges, i.e., an exhaust gas, "E" is removed from the vane engine through an exhaust port 25, also formed in the linear translation ring assembly plate and/or chamber ring 20.
The rotation of the rotor 10 in conjunction with the linear translation rings automatically sets the radial position of the vanes 12 at any rotor angle, producing a single contoured path as traced by the vane tips resulting in a unique stator cavity 21 shape that mimics and seals the path the vane tips trace.
The illustrated internal combustion engine employs a two-stroke cycle to maximize the power-to-weight and power-to-size ratios of the engine. The intake of the fresh air "I" and the scavenging of the exhaust gas "E" occur at the regions as shown in FIG. 1. One complete engine cycle occurs for each revolution of the rotor 10.
Fresh air can be mixed with fuel during the compression stage in alternate embodiments.
In operation, the vane engine shown in FIGS. 1 and 2 operates as follows.
The combustion charge is introduced into the vane chamber 14 through the intake "I" during an intake cycle 510. This combustion charge is preferably air or a fuel-air mix, and may have fuel added to it by the fuel injection device 27. The mixed fuel and air are then compressed in the vane chamber 14 during a compression cycle 520, as the rotor 10 continues its motion.
As the vane chamber 14 reaches the combustion residence chamber 26, a combustion cycle 530 is performed. During the combustion cycle 530, the air and fuel are combusted, causing a dramatic increase in heat and pressure. An initial combustion reaction is initiated by hot gases exiting the combustion residence chamber 26 and this jet is introduced to the vane chamber 14 during the combustion cycle 530 as a source of ignition. This combustion reaction then spreads circumferentially and radially throughout the vane chamber 14 until the air and fuel in the vane chamber have been substantially combusted. The combustion residence chamber is then automatically re-pressurized or primed with hot combusted gases for this combustion process to begin again with the subsequent vane cell. Sufficient time must be available for the combustion within the vane cell to be substantially complete and for the combustion residence chamber to be primed for the subsequent vane cell.
The combusted fuel and air are then expanded in an expansion cycle 540, and removed via an exhaust cycle 550.
FIG. 2 simply shows the operation of FIG. 1 in an `unrolled` state, in which the circular operation of the vane engine assembly is shown in a linear manner. The progression of the cycles 510, 520, 530, 540, and 550 can be seen quite effectively through FIG. 2.
In conventional designs spark plugs and glow plugs would initiate the combustion cycle 530. These methods of initiating combustion may be described as point ignition sources. Point ignition activates combustion of the fuel-air mixture at a local site in a given vane cell 14. However, the large surface area of the chamber wall surrounding the vane cell 14, results in a large distance that must be traversed by the propagating flame front before the combustion cycle can be complete.
As a result of this limitation and the low energy of the ignition method, point ignition devices such as glow plugs and spark plugs are unable to combust the ultra-lean mixtures necessary for ultra low emissions and best fuel economy. An important reason for the difficulty in achieving such flame propagation through an ultra-lean mixture is due to Damkohler number effects. For a discussion of Damkohler number effects on flame propagation, see "Blowout of Turbulent Diffusion Flames", J. E. Browdwell, W. J. A. Dahm, & M. G. Mungel, 20.sup.th Symposium (International) on Combustion/The Combustion Institute, 1984, pp. 303-310.
In short, however, point ignition devices lack the energy as well as the spatial and temporal exposure to successfully combust a premixed, ultra-lean fuel-air charge employing conventional hydrocarbon fuels within a rotary vane engine.
As a result of this, the use of a combustion residence chamber 26 has been proposed and employed. As noted above, the combustion residence chamber 26 is a small cavity strategically located within the chamber ring assembly 200. An orifice in the chamber ring assembly allows for communication of fuel-air mixtures between the point of maximum compression and the combustion residence chamber 26. This orifice may extend along the entire axial breadth of the vane cell, allowing for a line of combustion initiation, rather than simply a point source.
In operation, the combustion residence chamber 26 retains combustion gasses from one combustion cycle and uses them as an ignition source for the next combustion cycle. At the beginning of a given combustion cycle, a high-energy jet of hot combusted gases from the combustion residence chamber 26 rushes into the incoming vane cell 14 to initiate combustion and stir the reactants.
The combustion residence chamber 26 is thus not a point ignition source, but is a high-energy combustion device with greater spatial and temporal span, and so overcomes many of the limitations of spark plugs and glow plugs. It induces initial combustion reactions over a much larger zone with much greater energy and mixing effects. Furthermore, the hot jet orifice sweeps across the vane cell 14, providing excellent access and mixing to the reactants.
As a result of this, the combustion residence chamber system is capable of combusting much leaner premixed mixtures than would be possible with point ignition devices such as spark plugs, thereby permitting great reductions in pollution output and improvements in operating efficiency.
However, in order to obtain adequate mixing of the reactants the jet from the combustion residence chamber must move at high velocity, causing higher heat transfer and an associated efficiency loss. And while the combustion residence chamber works across a range of operating conditions, top engine speed may be limited by the requirement to promptly refill the combustion residence chamber with high pressure gas prior to the subsequent combustion cycle 530.
If the combustion residence chamber does not refill effectively prior to the subsequent vane cell's communication with the chamber, or for any other reason suffers a "flame-out," i.e., a loss of adequate temperature and/or pressure to complete a combustion cycle, then operational problems may occur. Addressing these problems in-process may require substantial mixture adjustments and/or the use of a supplemental ignition device, e.g., a spark plug, to maintain or reinitiate the sequential process of the combustion residence chamber 26.
An improved ignition source would offer the ability to fully, reliably, and robustly combust ultra-lean fuel-air mixtures, but without the requirement for the high velocity mixing jet and associated heat transfer as in the combustion residence chamber system. An improved combustion system would furthermore significantly reduce the sensitivity to engine speed and partial misfire associated with the requirement to fully refill the combustion residence chamber prior to the next combustion cycle, and would thereby enable more reliable combustion and higher engine speeds. An improved combustion system would therefore operate more efficiently, more reliably, and at higher engine speeds while achieving low pollution output.
Therefore, there exists a need for a combustion system within a rotary vane engine that is capable of robustly and reliably combusting ultra-lean mixtures across a wider range of engine speeds and conditions than achieved with the combustion residence chamber while simultaneously reducing heat transfer losses.